<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
    <%!
    Color getRandColor(int fc,int bc){//给定范围获得随机颜色
            Random random = new Random();
            if(fc>255) fc=255;
            if(bc>255) bc=255;
            int r=fc+random.nextInt(bc-fc);
            int g=fc+random.nextInt(bc-fc);
            int b=fc+random.nextInt(bc-fc);
            return new Color(r,g,b);
            }
    %>
    <%
    //设置页面不缓存
    response.setHeader("Pragma","No-cache");
    response.setHeader("Cache-Control","no-cache");
    response.setDateHeader("Expires", 0);

    // 在内存中创建图象
    int width=60, height=20;
    BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

    // 获取图形上下文
    Graphics g = image.getGraphics();

    //生成随机类
    Random random = new Random();

    // 设定背景色
    g.setColor(getRandColor(200,250));
    g.fillRect(0, 0, width, height);

    //设定字体
    g.setFont(new Font("Times New Roman",Font.PLAIN,18));

    //画边框
    //g.setColor(new Color());
    //g.drawRect(0,0,width-1,height-1);


    // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
    g.setColor(getRandColor(160,200));
    for (int i=0;i<155;i++)
    {
     int x = random.nextInt(width);
     int y = random.nextInt(height);
            int xl = random.nextInt(12);
            int yl = random.nextInt(12);
     g.drawLine(x,y,x+xl,y+yl);
    }

    // 取随机产生的认证码(4位数字)
    String sRand="";
    for (int i=0;i<4;i++){
        String rand=String.valueOf(random.nextInt(10));
        sRand+=rand;
        // 将认证码显示到图象中
        g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
        g.drawString(rand,13*i+6,16);
    }

    // 将认证码存入SESSION
    session.setAttribute("LoginCode",sRand);


    // 图象生效
    g.dispose();

    // 输出图象到页面
    ImageIO.write(image, "JPEG", response.getOutputStream());
    out.clear();  
    out = pageContext.pushBody();  

    %>